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Sunday, April 23, 2017

Pete would call this a DiFX: a transceiver that is Different from a BITX. This started with my effort to get an Si5351 working with a little 1 inch square OLED screen. Tom Hall AK2B helped me with the software (thanks Tom). Once I got that done, I figured I could build a simple receiver with a homebrew 11 MHz crystal filter, two NE602 chips, and an LM386 AF amplifier. That was working great, then Pete told me to turn it into a transceiver. I used some of Pete's boards (thanks Pete). The Epiphyte transceivers also use two NE602's, but they ingeniously switch the BFO and VFO between the two chips. I didn't switch the oscillators -- instead I switched the inputs and outputs of the two chips using two DPDT relays (thanks Jim). A third DPDT relay switches the antenna between T and R, and turns on and off the PA stage and the AF amplifier. This is a DIFX, but there is some BITX circuitry in there. The power amplifier stages are right out of the BITX Module, as is the AF amplifier (thank again Farhan). The only real problem I ran into had to do with the very low power out of the NE602 VFO mixer on transmit and the impedance matching between the NE602 and the PA chain. I had to increase the gain on the first RF amp (pre-driver) using ideas from Steve Weber's 40 meter SSB CW QST contest rig (thanks Steve). I experimented with various connections between the NE602 and the BP filter. Finally I got it going. The heat sink on this one is different too: it is just the chassis. The IRF 510 is bolted (insulated) to the aluminum box. I fired it up this afternoon and in spite of horrible conditions on 40, quickly had a nice rag chew with KJ4ZMV in Indiana. I haven't even built a mic amp yet! I am running the D-104 right into the NE602 balance modulator. There are no signs of unwanted modulation or spurs. FB! TRGHS! VIVE LA DIFFERENCE!

Bravo and Kudos -- see there is a life after a Bitx -- Congratulations on your DifX. Perhaps the next podcast we could feature this rig and discuss some of the issues you faced (as described in the posting). Again very nice --and no analog VFO to be seen anywhere. You are on the dark side.

Hi Bill, sounds great... any chance there is a schematic one can look at??? I have followed some of Steve Weber work... as I recalled he use an IC between the Ne602's on some of his rigs to switch in and out filter, I think??? I am not as gifted as you and Pete when it comes to design... but I do enjoy building circuits more than talking on the radio... looking forward to following this project of your... You do not know it but we go way back.. to when you first started doing pod cast... use to listen them on my MP3 player while at the gym on the treadmill...they help get thru the work out.. thanks for sharing 73 kg9dk..PS better email would be jab3739@sbcglobal.net

Yeah Bill! Show us how you solved the the mismatch between the NE602 and the PA chain. I'm having this Exact same problem with a NE602 rig. reaaally low power into the PA and my driver is now going into saturation mode and can't handle more collector current.John:"I do enjoy building circuits more than talking on the radio..." same here, except for CW.Awesome Work bill! 73.DanHK4DEI

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